Not better enough. DOn't spend the extra cash on 2gb, it just is not worth it.
As for VAPOR X, or TOXIC etc. they usually just mean the card has been customised a little - usually with a custom cooler and sometimes OC'd. I don't know more than that though as usually I just buy the basic card
My advice is to not spend extra on vapor-x or toxic, as you can easily surpass their overclocks on your own. The better coolers I guess are alright, probably (hopefully) quieter than the reference model, but IMO still not really necessary. My 5850s are greatly OCed and run idle very low ~40C maybe 45C with 15% fan speed. Gaming gets to maybe between 60-70C; I set my custom fan profile to ramp up a lot at those temps so by 70C it's running 70% speed which is noticeable but given that I'm gaming I don't notice it over the sound of gunfire or ambient music. But that's just me some people might find the sound a little annoying.